68 lines
1.9 KiB
Racket
68 lines
1.9 KiB
Racket
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#lang curly-fn racket
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(require "../lib.rkt")
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(define input
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(for/vector ([row (problem-input 11)])
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(for/vector ([col (string->list row)])
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(char->number col))))
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(define rows (vector-length input))
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(define cols (vector-length (vector-ref input 0)))
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(define total (* rows cols))
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(define (grid-ref grid row col)
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(vector-ref (vector-ref grid row) col))
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(define (grid-update! grid row col f)
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(vector-set! (vector-ref grid row) col (f (grid-ref grid row col))))
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(define (adjs grid row col)
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(for*/list ([r (range* (max 0 (sub1 row)) (min (sub1 rows) (add1 row)))]
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[c (range* (max 0 (sub1 col)) (min (sub1 cols) (add1 col)))])
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(cons r c)))
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(define (incr! octopodes)
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(for ([row (range rows)])
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(for ([col (range cols)])
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(grid-update! octopodes row col add1))))
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(define (flash! flashed octopodes)
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(for*/fold ([newly-flashed '()])
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([row (range rows)]
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[col (range cols)])
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(if (and (not (member (cons row col) flashed))
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(> (grid-ref octopodes row col) 9)
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(for ([adj (adjs octopodes row col)])
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(grid-update! octopodes (car adj) (cdr adj) add1)))
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(cons (cons row col) newly-flashed)
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newly-flashed)))
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(define (decharge! octopodes)
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(for ([row (range rows)])
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(for ([col (range cols)])
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(when (> (grid-ref octopodes row col) 9)
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(grid-update! octopodes row col (const 0))))))
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(define (step! octopodes)
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(incr! octopodes)
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(define flashes
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(let loop ([flashed '()])
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(let ([newly-flashed (flash! flashed octopodes)])
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(if (empty? newly-flashed)
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(length flashed)
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(loop (append newly-flashed flashed))))))
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(decharge! octopodes)
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flashes)
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(define part1
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(for/sum ([_ (range 100)])
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(step! input)))
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(define part2
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(let loop ([steps 101])
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(if (= (step! input) total)
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steps
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(loop (add1 steps)))))
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(show-solution part1 part2)
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